This invention relates to transparent plastic materials for optical use, and particularly to ocular devices which absorb ultraviolet radiation, and to their production from ultraviolet absorbing compounds, such as by copolymerizing the compounds with suitable reactive monomers.
Contact lenses containing compounds for blocking ultraviolet ("UV") light have been on the market for several years. Such lenses are useful to all who live in areas where bright sunlight is common. As UV radiation is likely to be a cause of cataracts and senile macular degeneration, everyone who wears contact lenses can benefit from the type which block this radiation. Younger persons, whose eye lenses transmit more ultraviolet radiation than do those of older persons, also should be concerned with providing additional protection.
Ultraviolet blocking lenses are especially useful for those who have had the natural lens of the eye removed, since the natural lens has UV absorption properties that help to protect the interior of the eye. Hence, UV absorbing intraocular lenses (IOLs) are also highly desirable, since such lenses are implanted in place of the eye's natural lens.
Loshaek discovered the use of polymerizable UV absorbing compounds for producing contact and intraocular lenses in the early 1970's, e.g., as shown in U.S. Pat. No. Re. 33,477. More recently, substituted 2-phenyl benzotriazole compounds having a polymerizable acrylic group have been used to produce contact lenses, e.g., as in U.S. Pat. No. 4,716,234 to Dunks et al. The UV absorption technology has been applied primarily to rigid, gas permeable lenses; most commercially available soft lenses do not contain UV absorbers.
Hydrogels are desirable for use in lenses, particularly IOLs. However, because of their hydrophilic nature and expanded structure, it has been difficult to incorporate UV absorbing compounds into hydrogels. Prior art UV absorbers are generally hydrophobic and have limited solubility in hydrogels. Due in part to this limited solubility, it has been difficult to copolymerize UV absorbers with hydrogel forming monomers. UV absorbers are preferably copolymerized, rather than physically entrapped within the hydrogel, to prevent the absorber from being leached out of the UV absorbing hydrogel when the hydrogel is in the aqueous environment of the eye or stored in solution.
In addition to problems of incorporation of UV absorbers into hydrogels, UV absorbers having the required characteristics such as UV absorption between 300-400 nm and hydrolytic stability have been difficult to synthesize.
Recently, Collins, et al. discovered a new class of benzotriazoles that are useful in soft contact lenses, as shown in U.S. Pat. No. 5,637,726. The compounds absorb UV light very well at the upper end of the UV spectrum. These benzotriazoles copolymerize well into hydrogel polymers without the problems of leaching out. Also, effective amounts of these benzotriazoles incorporated into the contact lens polymer do not negatively affect the properties of the polymer. Also, these compounds increase the refractive index and optic potential of the contact lenses, allowing for thinner lenses with enhanced oxygen permeability. These compounds also have a higher cut-off, up to 400 nm, to block more light in the UVA range.
While contact lenses containing a UV absorbing compound are now commercially available, these lenses do not block all of the UV light from entering the eye, and typically only block about 90% of the entire UV range. The UV range is generally broken in to two subranges, known as UVA and UVB. ANSI Class 1 specifications for UV absorption require an average percent transmittance of less than 1.0% at 280-315 nm (UVB range) and only less than 10% at 316-380 nm (UVA range). Commercially available UV absorbing contact lenses do not meet this standard.
The difficulty in obtaining a UV blocking contact lens that meets Class 1 standards by using a benzotriazole, as described by Collins et al., is that one has to use so much benzotriazole that the lens also absorbs significant amount of light at the upper end of the UVA range and into the visible light range. This results in an observable yellowish tint in the contact lens, which is not appealing to consumers. More importantly, this yellowish tint throws off the cosmetic appearance of colored contact lenses. In addition, too much benzotriazole, or other UV absorbing compound, can adversely affect the properties of the lens polymer, such as durability, flexibility, hydrophilicity, stability to sterilizing regimes, etc. Also, the compound may be present in too high quantities for all of it to covalently bond with the other monomers during the polymerization, resulting in excessive residual monomer content that may gradually leach out during use.
Hung et al., U.S. Pat. No. 4,963,160, proposes a solution to some of these problems by bonding two different UV absorbing compounds that each have a different UV absorbing spectra onto a triazine derivative, which is then applied as a coating onto a polymeric lens. The UV absorbers are preferably selected to provide a UV absorbing agent with the broadest UV absorption range possible. Hung et al. disclosed embodiments of these UV absorbing agents that include p-aminobenzoic acid and a benzotriazole, or p-aminobenzoic acid and a benzophenone. The use of this UV absorbing agent has certain limitations because the UV absorbing compounds can only be used in a one-to-one mole ratio, so that the UV absorption spectra of the lens cannot be optimized. Also, there are difficulties to achieve consistent coating thicknesses.